1. Field of the Invention
The present invention relates to a recording member for the electrographic recording of toner images thereon and to a coating for the recording member, which coating provides the member with electrical, optical, and durability characteristics useful for the recording process.
2. Description of the Prior Art
Kotz, U.S. Pat. No. 3,816,840 discloses an electrographic recording process and apparatus in which a dielectric recording member is arranged between two electrodes. Magnetically adhered to one of the electrodes is electronically conductive toner powder. The toner powder provides an electrically conductive path between the electrode to which it is bound and the adjacent surface of the dielectric member. A voltage is applied to the electrodes for a time and of a magnitude sufficient to generate a force pattern on the toner which enables toner deposition on the recording member in accordance with the force pattern. The force pattern is generated directly on the toner rather than on the recording member, which is passive in the operation of the apparatus disclosed in the patent.
Resistance to mechanical damage, abrasion, and wear are important characteristics for the receptor surface of a recording member employed in a process where an appreciable number of images are required to be applied thereto and removed therefrom. These characteristics of durability can be judged by subjecting a receptor surface to repeated cycles of the process and observing the images produced for signs of catastrophic failure or gradual deterioration. The number of cycles completed while retaining the ability to produce images meeting the acceptance criteria is a measure of the surface's durability.
It is often desirable to apply the toner to a dielectric recording member which has a background color which offers high contrast to the toner powder. For example, if the contrast between toner powder and the recording member to which it is applied were sufficiently high, e.g. 0.6 optical density units, the recorded information could be read directly or indirectly, or even copied by optical means, all with high fidelity and high resolution. Then, the untransferred, unfixed toner powder could be removed from the recording member and new information could be displayed thereon. A system employing a recyclable toner powder could then be designed to optimize the quality of the displayed image without regard to its transfer and fixing properties, or to the cost of depleting the toner powder with each copy. Alternatively, the toner powder could be fixed to the recording member if so desired.
Anodized aluminum has been used as a recording member for the electrographic recording apparatus described herein. An aluminum oxide surface that has the appropriate electrical response can be formed on an aluminum substrate by anodization or other conventional means. However, it is well known that such surfaces change over time, particularly when subjected to environments having high relative humidity. This change may adversely affect the electrical characteristics of the aluminum oxide surface. Furthermore, in environments of high relative humidity, aluminum oxide surfaces tend to collect a film of moisture that must be removed by special means to assure a stable electrographic process. Finally, anodized aluminum and other such surfaces do not have the optical properties desirable for certain desirable applications of the process disclosed in the Kotz patent.
Other materials for a receptor surface which have appropriate electrical characteristics for use in a rapid cycle electrographic recording process generally are unable to withstand the mechanical abuse resulting from flexing, cycling, and the application and removal of toner powder.
A polyester film bearing an appropriate pigment can provide the desired contrast between recording member and toner powder. However, a polyester film, or a film prepared from another dielectric organic resin, when applied to a conductive grounding surface, will generally allow charge to build up resulting in excessive backgrounding and ghosting.
Over a period of use, e.g. about 100 cycles of image formation and image removal from the recording member, residual charge builds up within the dielectric recording member. This build-up of charge results in excessive backgrounding and ghosting, making the recording member useless for further image formation.
Thus, it can be seen that selection of a recording member and dielectric coating thereof for use with a recyclable imaging powder may be constrained by at least three factors:
(1) Charge must be essentially completely removed from the recording member within one operating cycle of the process; PA1 (2) Durability properties of the recording member must be sufficient in order to allow the process to be economically feasible; PA1 (3) Contrast between the toner powder and the recording member can be specified to be high, e.g. at least 0.6 optical density units.
Although it is relatively simple to provide a recording member that fulfills any one of the three foregoing constraints, satisfaction of all three of them simultaneously has heretofore proved to be extremely difficult. The problem of charge build-up has presented great difficulty in finding suitable materials for recording members. True resistive materials, e.g. most polymeric materials, have the undesirable tendency of trapping charges in their structural matrices. At the voltages and cycle durations of the recording process described in Kotz, the build-up of trapped charges occurs over a period of about 100 cycles. Removal of the trapped charges would require a relatively long period of time.